This invention relates to a tensioner which provides a fixed tension to a chain or a timing belt which drives a cam shaft or an engine of an autocycle or a vehicle.
A tensioner such as a chain tensioner, a belt tensioner or the like is used for maintaining a fixed tension by urging the chain or the belt in a fixed direction when the chain or the belt slackens by extension or friction thereof during the use.
FIG. 6 shows a conventional tensioner disclosed in U.M. laid open No. 62 (1987)-19015. The main parts thereof are constituted by:
a cylindrical casing 1 secured approximately vertically with bolt holes 11a, 11a for fixing, a rotary body 2 having a shaft rotatively inserted into the casing 1, an urging body 3 which propels by rotation of the rotary body 2 screwed with a male screw portion 2a formed at the top end portion to the rotary body 2, a spring (torsion spring) 4 which provides a torque to the rotary body 2 outwardly inserted therethrough, and a bearing 5 which performs a restrictive rotation of the urged body 3 fixed to the casing 1 having a non-circular bearing hole which penetrates the urged body 3.
When the urged body 3 abuts against the chain, belt or the like in a state wherein the rotation energy is storaged in the spring by rotating the rotary body 2 in such a constitution, the rotary body 2 rotates by aid of the spring 4 and the torque is transmitted to the urged body 3.
However, since the urged body 3 is restricted the rotation thereof by the bearing 5, the torque of the urged body 3 converts to a propelling power to urge the chain, belt or the like. By this, the chain or the belt can be maintained a fixed tension without deflection of the chain, belt or the like.
In such a tensioner, in order to prevent the invasion of dusts and the like into the casing 1 or the leakage of lubricating oil filled therein, the inner portion of the casing 1 must be tightly closed. For this purpose, the base portion (lower end portion) of the casing is screwed with seal bolts 7, and an elastic bellows 6 is covered between the top end portion (upper end portion) of the casing and the urged body 3 which propels and drives. The top end of such bellows 6 is secured to the urged body 3 with a spring band 8, and the lower end portion thereof is connected with a cap 9 forcibly inserted into the casing 1 to close between the urged body 3 and the casing 1. An air-escaping hole 11 having a "T" type is formed to the urged body 3 positioning at the upper portion of the bellows 6. The air-escaping hole 11 is formed at a position higher than the liquid surface of the lubricating oil within the casing 1 to connect the inner portion of the casing 1 and the outer portion thereof. The air-escaping hole 11 prevents a negative pressure due to the change of volume within the casing according to propelling of the urged body 3. By this, the propelling of the urged body 3 can be securely performed.
Further, the numeral 10 in FIG. 6 is a stopper which locks the propelling of the urged body 3 and is removed properly after installing the tension.
In the conventional tensioner, there necessitates an air-escaping hole 11 which prevents a negative pressurization of the inside of the casing 1. Therefore, there exists a limit in an attaching direction of the tensioner. In other words, it is necessary to prevent the discharge of the inner lubricating oil outwards through the air-escaping hole 11. For this purpose, it is necessary to provide the air-escaping hole 11 in a vertical direction positioned at an upper portion or in a slightly inclined direction. Accordingly, it is not only impossible to provide it in a horizontal direction, but also the attached position is defined. Further, the same consideration is necessary in conveyance and packing, and inconvenient in treatment. Furthermore, even if such consideration is taken, there often occurs the leakage of the lubricating oil from the air-escaping hole 11 by the expansion and the vibration due to the rise of the temperature and a sufficient measure against the oil leakage can not be taken.